Re: [PATCH v2 1/2] powerpc: Avoid signed to unsigned conversion in set_thread_tidr()

Vaibhav Jain [off-list ref] writes:

There is an unsafe signed to unsigned conversion in set_thread_tidr()
that may cause an error value to be assigned to SPRN_TIDR register and
used as thread-id.

The issue happens as assign_thread_tidr() returns an int and
thread.tidr is an unsigned-long. So a negative error code returned
from assign_thread_tidr() will fail the error check and gets assigned
as tidr as a large positive value.

To fix this the patch assigns the return value of assign_thread_tidr()
to a temporary int and assigns it to thread.tidr iff its '> 0'.

The patch shouldn't impact the calling convention of set_thread_tidr()

But it does? I'm really confused.

Please fix and resend.

cheers

 int set_thread_tidr(struct task_struct *t)
 {
+	int rc;
+
 	if (!cpu_has_feature(CPU_FTR_ARCH_300))
 		return -EINVAL;

                ^
                -ve error

 
 	if (t != current)
 		return -EINVAL;

                ^
                -ve error

 
-	t->thread.tidr = assign_thread_tidr();
-	if (t->thread.tidr < 0)
-		return t->thread.tidr;

                ^
                -ve error

Yes I know we never hit that case because of the bug, that is what this
patch should be fixing, and only that.

-
-	mtspr(SPRN_TIDR, t->thread.tidr);
+	rc = assign_thread_tidr();
+	if (rc > 0) {
+		t->thread.tidr = rc;
+		mtspr(SPRN_TIDR, t->thread.tidr);
+	}
 
-	return 0;

Success == 0

+	return rc;

Success == +ve TIDR

 }

cheers